The use of fossil fuel such as oil has generated a serious pollution problem and induced a global warming problem. In order to overcome such problems, hydrogen has been receiving attention as an alternative fuel. The hydrogen can be created from water that unlimitedly exists in the earth. The hydrogen is transformed back to the water again after generating energy.
Therefore, the water will not be dried up forever. When the hydrogen is combusted, pollutants are not generated except the generation of the extremely small amount of nitrous oxide. Accordingly, the hydrogen has been considered as clean energy. Also, the hydrogen can be transformed to various types of energy. For example, the hydrogen is transformed to heat energy through combustion. The hydrogen is also transformed to mechanical energy through an internal combustion engine, or to electrical energy through reaction with oxygen as fuel battery.
However, the hydrogen has not been widely used although the hydrogen has many advantages as described above. One of reasons for not widely using the hydrogen is the difficulty of safely storing the hydrogen at high density. Accordingly, there have been many researches in progress for developing a hydrogen storage medium and a hydrogen storage method for abruptly increasing hydrogen storage capacity in order to use the hydrogen as an energy source.
As a hydrogen storage method according to the related art, a liquid hydrogen storing method, a gaseous hydrogen storing method, an alloy based hydrogen storing method, and a carbon nanotube based hydrogen storing method have been introduced. The liquid hydrogen storing method and the gaseous hydrogen storing method may be dangerous because the liquid hydrogen and the gaseous hydrogen are highly explosive at normal temperature. Also, the liquid hydrogen storing method and the gaseous hydrogen method have the disadvantage of an expensive storage cost. The alloy based hydrogen storing method stores hydrogen in an alloy.
Although it can safely store the hydrogen, it has a limitation of commercialization because of a heavy weight and a small hydrogen storage surface area. The carbon nanotube based hydrogen storing method stores hydrogen in carbon nanotube. Since the carbon nanotube has a wider surface area than the alloy, more hydrogen can be stored using the carbon nanotube based hydrogen storing method. Carbon material in the carbon nanotube is very chemically stable. Therefore, it is difficult to absorb the hydrogen into the carbon nanotube and to desorb the hydrogen from the carbon nanotube after the hydrogen gas is absorbed to the carbon nano tube. Therefore, the hydrogen storage capacity may become reduced.